Spectrometer with a relay lightpipe

ABSTRACT

A lightpipe is coupled to a spectrometer based on a laterally variable optical filter. The lightpipe may be used for both guiding the illuminating light towards a sample and collecting light reflected or emitted by the sample upon illumination, for spectral measurements at a distance from the sample afforded by the lightpipe. The lightpipe may include a slab of homogeneous transparent material for unconstrained bidirectional propagation of light in bulk of the material. The lightpipe may be solid, hollow, or sectioned for separated guiding of the illuminating and the reflected light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/710,095, filed May 12, 2015 (now U.S. Pat. No. 9,885,655), which is acontinuation-in-part from U.S. patent application Ser. No. 14/079,280,filed Nov. 13, 2013 (now U.S. Pat. No. 9,234,839), which claims priorityfrom U.S. Provisional Patent Application No. 61/725,923, filed Nov. 13,2012, and 61/784,811, filed Mar. 14, 2013. U.S. patent application Ser.No. 14/710,095 claims priority from U.S. Provisional Patent ApplicationNo. 61/992,082, filed May 12, 2014; the disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to optical test and measurement, and inparticular to portable optical spectrometers.

BACKGROUND

A laterally variable optical filter (LVF) may include a transmissionoptical filter having a transmission wavelength varying in a transversedirection across a surface of the filter. A compact optical spectrometermay be constructed by coupling a photodetector array to an LVF. When theLVF surface is illuminated with light reflected by the sample, lightportions at individual wavelengths are selectively transmitted throughthe LVF and detected by individual pixels of the photodetector array. Asa result, a reflection spectrum of the sample may be obtained. Aminiature light source may be provided in an LVF-based spectrometer forilluminating a sample, enabling quick, on-the-spot reflection spectralmeasurements.

Due to their miniature size and small weight, LVF-based spectrometersmay be constructed in handheld configuration, making them suitable foruse in a variety of test and measurement applications. It is sufficientto bring such a handheld LVF-based spectrometer in close proximity withthe sample, and to press a thumb-operated button on the back of thespectrometer to quickly (within seconds, or even less than a second)obtain a reflection spectrum. Other types of spectra, e.g. fluorescence,transmission, etc., may also be obtained with a suitable configurationof the light source.

A direct contact between the handheld spectrometer and the sample may beundesirable. For instance, chemically aggressive samples, extremely hotor cold samples, bio-hazardous samples, etc., may damage the compactspectrometer or endanger the user. In other applications, such as foodprocessing, a direct physical contact may be undesirable for hygienicreasons. For applications such as these, a remote spectra collection maybe preferable.

To obtain a spectrum from a safe distance, the illuminating light may beformed into a parallel or converging beam of light by a lens-based ormirror-based collimator, so as to concentrate the illuminating light onthe sample. A mirror or lens, or a lens system, may be used to remotelycollect light reflected by the sample. Alternatively, a pair of opticalfibers may be used to bring the illuminating light to the sample, and toguide the reflected light back into a spectrometer for a spectralmeasurement.

Free-space or fiber-guided illumination delivery and light collectionsystems have some drawbacks. For repeatability purposes, a free-spacecollection system needs to be placed at a pre-defined distance from thesample, which may not be convenient, or may even be unfeasible whenholding the spectrometer by hand. Light collection systems based onoptical fibers typically require precision optical alignment forcoupling light into the illuminating fiber, and may require dedicatedoptics, so-called “optical head”, for coupling the reflected light intoa core of the light collection fiber. Transmission of a fiber bundle maydepend on its bend radius, requiring re-calibration if the fiber bundleis re-shaped or bent at a different radius. Furthermore, most opticalfibers are fragile and expensive, and may require replacement upondamage of sensitive fiber tips caused by chemically aggressive, hot,cold, or abrasive samples.

SUMMARY

In accordance with an aspect of the disclosure, a length of a lightpipe,herein termed a “relay lightpipe”, may be used for conductingilluminating light to the sample, and for collecting (relaying) lightreflected or emitted by the sample back to an LVF-based spectrometer. Arelay lightpipe may include a slab of a transparent material forunconstrained propagation of light in bulk of the material, or it may behollow. A relay lightpipe may also be straight or pre-curved. Due torelative insensitivity of an LVF-based spectrometer to a solid angle andspot size of the emitted or reflected light, meaningful spectral datamay be obtained even when a same slab of transparent material is usedfor guiding both the illuminating and reflected light in oppositedirections, so that the optical paths of the illuminating and reflectedlight overlap in the slab. In other words, the illuminating light may beguided by the relay lightpipe towards the sample, and the reflectedlight may be guided by the relay lightpipe towards the spectrometer, sothat optical paths of the illuminating light and the reflected light mayoverlap in the relay lightpipe. The length of the relay lightpipe may beselected to be sufficiently long to enable a direct illumination andcollection of light reflected or emitted by a hot or cold sample, whilekeeping temperature-sensitive spectrometer electronics away from the hotor cold sample.

In accordance with an aspect of the disclosure, there is provided anapparatus for obtaining an optical spectrum of a sample, the apparatuscomprising:

a spectrometer comprising: a housing comprising an outer surface; alight source within the housing for illuminating the sample withilluminating light; and a spectral engine within the housing forobtaining the optical spectrum of the sample illuminated with theilluminating light, wherein the spectral engine comprises a laterallyvariable optical filter coupled to a photodetector array, wherein thelight source and the spectral engine are optically coupled to an openingor transparent window in the outer surface; and

a relay lightpipe extending between proximal and distal ends thereof andconfigured for unconstrained propagation of the illuminating light inbulk of the relay lightpipe from the proximal to the distal end when theproximal end is optically coupled to the light source and the spectralengine via the opening or transparent window, and wherein the distal endis configured for contacting or inserting into the sample;

wherein the relay lightpipe is configured for collecting signal lightemanating from the sample when the sample is illuminated with theilluminating light via the relay lightpipe, and for unconstrainedpropagation of the signal light in bulk of the relay lightpipe back fromthe distal end to the proximal end, for delivery to the spectral engine,thereby enabling the spectrometer to obtain the optical spectrum of thesample at a distance from the sample.

In one embodiment, the relay lightpipe may include a slab of homogeneoustransparent material extending between the proximal and distal ends,such that optical paths of the illuminating and signal light at leastpartially overlap in the slab. In another embodiment, the relaylightpipe may be sectioned, i.e. the relay lightpipe may include firstand second slabs of homogeneous transparent material extending betweenthe proximal and distal ends and running adjacent and parallel to eachother. The first slab may be configured for propagating the illuminatinglight therein from the proximal end to the distal end, and the secondslab may be configured for propagating the signal light therein from thedistal end to the proximal end. The distal end of the relay lightpipemay be chiseled or lensed, for focusing the illuminating light on thesample, and for collecting the signal light from the sample.

For samples including a granular material such as seeds, powders, etc.,material capable of mixing or flowing, or for samples comprising fluids,including fluid suspensions, emulsions, etc., the apparatus may includea container for holding the granular or fluid material, and a vibrationtransducer for vibrating the granular or fluid material. For example,the vibration transducer ma be operably coupled to the container forvibrating the container. The container may include an opening forinserting the relay lightpipe into the granular or fluid material forobtaining an optical spectrum of the granular or fluid material, whilethe vibration transducer vibrates the container, thereby causing movingand mixing of the granular or fluid material. The moving and mixing ofthe granular or fluid material may help average reflection spectra beingobtained, thereby making the reflection spectra less dependent on arandom configuration of the granular or fluid material at the spot ofillumination.

In accordance with the disclosure, there is further provided anapparatus for obtaining an optical transmission spectrum of a samplecomprising a granular or fluid material, the apparatus comprising:

a spectrometer comprising a housing comprising an outer surface and aspectral engine within the housing for obtaining a light spectrum of thesample illuminated with the illuminating light, wherein the spectralengine comprises a laterally variable optical filter coupled to aphotodetector array, wherein the spectral engine is optically coupled toan opening or transparent window in the outer surface;

a relay lightpipe extending between proximal and distal ends thereof andconfigured for unconstrained propagation of light in bulk of the relaylightpipe between the proximal and distal ends, wherein the relaylightpipe is connectable to the housing so that the proximal end isdisposed against the opening or transparent window, for optical couplingthe relay lightpipe to the spectral engine, and wherein the distal endis configured for contacting or inserting into the granular or fluidmaterial;

a container for holding the sample, wherein the container comprises awindow at a bottom thereof;

a vibration transducer operably coupled to the container for vibratingthe granular or fluid material; and

a light source optically coupled to the window, for illuminating thesample with illuminating light through the window while the vibrationtransducer vibrates the container thereby causing moving and mixing ofthe granular or fluid material;

wherein the relay lightpipe is configured for collecting signal lightemanating from the mixing and moving granular or fluid materialilluminated with the illuminating light, and for conducting the signallight back from the distal end to the proximal end, for delivery to thespectral engine, thereby enabling the spectrometer to obtain thetransmission spectrum of the sample at a distance from the sample.

In one embodiment, the relay lightpipe comprises a first opening thereinextending therethrough in a direction transversal to the illuminatinglight, the apparatus further comprising a calibration element insertableinto the first opening, wherein the calibration element comprises areflectance reference section for registering with the first openingwhen the calibration element is inserted into the first opening, so asto reflect the illuminating light back to the proximal end of the relaylightpipe for detection by the spectrometer.

In accordance with the disclosure, there is further provided a methodfor obtaining an optical spectrum of a sample, the method comprising:

bringing near the sample, contacting the sample, or inserting into thesample a relay lightpipe of a spectrometer,

wherein the spectrometer comprises a housing comprising an outersurface, a light source within the housing for illuminating the samplewith illuminating light, and a spectral engine within the housing forobtaining the optical spectrum of the sample illuminated with theilluminating light, wherein the spectral engine comprises a laterallyvariable optical filter coupled to a photodetector array, wherein thelight source and the spectral engine are optically coupled to an openingor transparent window in the outer surface;

wherein the relay lightpipe extends between proximal and distal endsthereof and is configured for unconstrained propagation of light in bulkof the relay lightpipe between the proximal and distal ends, wherein therelay lightpipe is optically coupled to the light source and thespectral engine via the opening or transparent window;

conducting the illuminating light in the relay lightpipe from theproximal end to the distal end thereof for illuminating the sample,

collecting signal light emanating from the sample illuminated with theilluminating light wherein the signal light is collected via the distalend of the relay lightpipe,

conducting the signal light back from the distal end to the proximal endand further to the spectral engine via the relay lightpipe; and

obtaining the optical spectrum of the sample at a distance from thesample.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will now be described in conjunction with thedrawings, in which:

FIG. 1A illustrates a schematic side cross-sectional view of anapparatus of the present disclosure for obtaining an optical spectrum ofa sample, the apparatus including a homogeneous relay lightpipe havingflat ends;

FIG. 1B illustrates a ray-tracing simulation of the apparatus of FIG.1A;

FIG. 1C illustrates a three-dimensional view of the ray-tracingsimulation of FIG. 1B;

FIG. 1D illustrates a plan view of an embodiment of a relay lightpipefor use in the apparatus of FIG. 1A;

FIG. 2 illustrates a three-dimensional view of a ray-tracing simulationof an apparatus for obtaining an optical spectrum of a sample, theapparatus including a relay lightpipe having a lens at the distal end;

FIG. 3A illustrates a schematic side cross-sectional view of anapparatus for obtaining an optical spectrum of a sample, the apparatusincluding a sectioned chiseled relay lightpipe;

FIG. 3B illustrates a ray-tracing simulation of the apparatus of FIG.3A;

FIG. 4A illustrates a schematic side cross-sectional view of anapparatus for obtaining a reflection optical spectrum of a granularsample;

FIG. 4B illustrates a schematic side cross-sectional view of anapparatus for obtaining a transmission optical spectrum of a granularsample;

FIG. 5A illustrates a schematic side cross-sectional view of anapparatus for performing a spectral measurement of a flowing material;

FIG. 5B illustrates a schematic side cross-sectional view of a variantof the apparatus of FIG. 5A including an optical fiber bundle;

FIGS. 6A and 6B illustrate a self-calibrating variant of the apparatusof FIG. 1A; and

FIG. 7 illustrates a method of the present disclosure for obtaining anoptical spectrum of a sample.

DETAILED DESCRIPTION

While the present teachings are described in conjunction with variousembodiments and examples, it is not intended that the present teachingsbe limited to such embodiments. On the contrary, the present teachingsencompass various alternatives and equivalents, as will be appreciatedby those of skill in the art.

Referring to FIGS. 1A, 1B, and 1C, an apparatus 10 for obtaining anoptical spectrum of a sample 11 may include a spectrometer 12 having ahousing 13 (FIG. 1A). The apparatus 10 may further include a relaylightpipe 14, which may be attached to the housing 13 by means of anoptional coupler 15. The optical coupler 15 may include, for example, athreaded opening 15A in the housing 13. The spectrometer 12 may includea pair of light bulbs 16 disposed within the housing 13, forilluminating the sample 11 with illuminating light 17. Another lightsource or sources, e.g. light emitting diodes (LED), may be used insteadof the pair of light bulbs 16. One light bulb 16 may be used. Thespectrometer 12 may further include a spectral engine 6 disposed withinthe housing 13, for obtaining the optical spectrum of the sample 11. Thespectral engine 6 may include a laterally variable optical filter (LVF)9 coupled to a photodetector array 8. The light bulbs 16 and thespectral engine 6 may be optically coupled to the opening 15A or anoptional transparent window, not shown, in an outer surface 13A of thehousing 13. Due to the compactness of the spectral engine and thephotodetector array 8, the spectrometer 12 may be portable or handheld,and may have dimensions of less than 15 cm×15 cm×15 cm, and having aweight of less than 2 kg.

The relay lightpipe 14 extends between its proximal 14A and distal 14Bends. The proximal end 14A of the relay lightpipe 14 may be opticallycoupled to the opening 15A in the outer surface 13A. The distal surface14B may be optically coupled to the sample 11. The relay lightpipe 14may be configured to provide unconstrained propagation of light in bulkof the relay lightpipe 14 between the proximal 14A and distal 14B ends.In other words, light may propagate in the relay lightpipe as a free,non-guided wave, being limited only by reflections from walls i.e.without any guiding elements having a non-uniform refractive index forguiding light, such as optical fibers.

The function of the threaded coupler 15 is to affix the relay lightpipe14 to the housing 13 so that the proximal end 14A of the relay lightpipe14 is disposed within or adjacent the opening 15A or the optionalwindow, for optical coupling the relay lightpipe 14 to the light bulbs16 and the spectral engine 6. Other types of couplers, e.g. a cam-basedcoupler, a friction-based coupler, a lockable ledge-based coupler, etc.may be used instead of the threaded coupler 15. The purpose of thethreaded coupler 15, or a similar coupler, may be to quickly replace therelay lightpipe 14 with another relay lightpipe 14 of a different lengthor shape, or the same length L e.g. when the previous relay lightpipe 14becomes contaminated or damaged in the process of measuring the opticalspectrum of the sample 11.

When affixed, the relay lightpipe 14 is optically coupled to the lightbulbs 16 and the spectral engine 6. The relay lightpipe 14 may beconfigured for conducting the illuminating light 17 from the proximal14A end to the distal end 14B. The proximal end 14A of the relaylightpipe 14 may include a substantially flat surface for opticallycoupling to the opening 15A, or a transparent window if any, in theouter surface 13A of the housing 13. The distal end 14B of the relaylightpipe 14 may be configured for bringing near, contacting, and/orinserting into the sample 11, so that signal light 18 emanating from thesample 11 upon illumination with the illuminating light 17, may becollected by the distal end 14B of the relay lightpipe 14. The collectedsignal light 18 may propagate back from the distal end 14B to theproximal end 14A of the relay lightpipe 14, for delivery to the spectralengine 6 via an optional tapered light pipe (TLP) 7. The TLP 7 mayextend between narrow 7A and wide 7B ends of the TLP 7. The wide end 7Amay be optically coupled to the LVF 9, and the narrow end 7B may bedisposed proximate the opening 15A, or window if provided, in the outersurface 15 of the housing 13. A more detailed description of thespectrometer 12 is provided in U.S. patent application Ser. No.14/079,280, which is incorporated herein by reference.

The spectrometer 12 may obtain an optical spectrum of the sample 11,e.g. a reflection or fluorescence spectrum. The relay lightpipe 14enables the optical spectrum to be measured from a distance from thesample 11 approximately equal to a length L of the relay lightpipe 14(FIG. 1C). In one embodiment, the length L is at least 8 mm to ensure anadequate distance to a food sample, for example. The length L may beover 50 mm, and even over 200 mm in some embodiments e.g. where achemically active, hot, or cold samples need to be measured. The lengthL may be limited by an absorption loss in the bulk of the relaylightpipe 14, and/or by a surface scattering or transmission loss ofreflecting surface(s) of the relay light pipe 14.

The relay lightpipe 14 shown in FIG. 1C has a circular cross-sectionhaving a cylindrical outer wall 14C extending between the proximal 14Aand distal 14B flat surfaces. The relay lightpipe 14 is not limited to acircular cross-section, for example the relay lightpipe 14 may haveoval, rectangular, or polygonal cross-section. The relay lightpipe 14may have a diameter or a lateral size of at least 2 mm, more preferablyat least 5 mm. The relay lightpipe 14 shown in FIGS. 1A to 1C may be aslab of a homogeneous transparent material extending between theproximal 14A and distal 14B substantially flat optical surfaces. Glass,acrylic, or another transparent material may be used. In one embodiment,the relay lightpipe 14 has a large enough refractive index, e.g. 1.6 ormore, so that a substantial portion, e.g., at least 80%, of opticalpower of the illuminating 17 and the signal 18 light entering the relaylightpipe 14 and propagating between the proximal 14A and distal 14Bflat surfaces, is retained in the relay lightpipe 14 by total internalreflection (TIR) from the outer wall 14C. Rays at angles of incidencesmaller than a TIR, critical angle may escape the relay lightpipe 14. Toimprove overall reflectance, the outer wall 14C may be mirrored toprovide near 100% reflectivity even for the rays at small angles ofincidence.

The relay lightpipe 14 may have more than one wall. For example, therelay lightpipe 14 may have triangular, rectangular, or polygonal shapedcross section, such that the relay lightpipe 14 may have three, four,and more outer walls. Furthermore, the relay lightpipe 14 may be hollowand optionally include a reflective inner wall. The relay lightpipe 14may also include a permanently bent section, not shown, between,proximal 14A and distal 14B ends of the relay lightpipe 14.

In the embodiments shown in FIGS. 1A to 1C, the relay lightpipe 14 has across-section that is substantially constant between the proximal 14Aand distal 14B ends of the relay lightpipe 14. The relay lightpipe 14may also be tapered. Referring to FIG. 1D with further reference toFIGS. 1A to 1C, a tapered relay lightpipe 19 is shown with the lightbulbs 16 and the TLP 78. The tapered relay lightpipe 19 (FIG. 1D) widensin going from its proximal 19 a to the distal 19B end; that is, a widthD of a cross-section 19C of the tapered relay lightpipe 19 may increasein going from the proximal 19 a to the distal 19B ends. The taperedshape may facilitate obtaining a more averaged spectrum of the sample11, because a larger area of the sample 11 may be illuminated due to thewider distal end 19B, and the signal light 18 may be accordinglycollected from the larger area of the sample 11. The tapered relaylightpipe 19 may function as a non-imaging concentrator of light, forexample a compound parabolic concentrator of light. To that end, asidewall 19D of the tapered relay lightpipe 19 may be curved as shown inFIG. 1D, so that the width D of the cross-section 19C increases in anon-linear fashion in going from the proximal 19 a to the distal 19B endof the tapered relay lightpipe 19.

Optical paths of the illuminating 17 and signal 18 light may overlap inthe slab 14, as shown in the simulations of FIGS. 1B and 1C. Eventhought the optical paths of the illuminating 17 and signal 18 light maypartially overlap, the spectral engine 6 is able to obtain a reflectionspectrum with a good, e.g. better than 20 dB, signal-to-noise ratio.This unexpected and advantageous feature may be related to a relativeinsensitivity of an LVF-based spectrometer, such as the spectrometer 12,to a solid angle of the signal light 18, e.g. emitted or reflectedlight, at the LVF 9. The TLP 7 has a property of reducing the solidangle as the signal light 18 propagates from the narrow end 7A to thewide end 7B of the TLP 7, which further relaxes the requirement of thesolid angle of the signal light 18.

Referring now to FIG. 2 with further reference to FIGS. 1A-1C, anapparatus 20 for obtaining an optical spectrum of the sample 11 issimilar to the apparatus 10 of FIGS. 1A-1C. One difference of theapparatus 20 of FIG. 2 is that the slab 14 may end with a lens element26 optically coupled to the distal end 14B far focusing the illuminatinglight 17 on the sample 11, and/or for collecting the signal light 18from the sample 11. In one embodiment, instead of the lens element 26,the distal end 14B itself may be chiseled or lensed.

Turning now to FIGS. 3A and 3B with further reference to FIGS. 1A-1C andFIG. 2, an apparatus 30 for obtaining an optical spectrum of the sample11 is similar to the apparatus 10 of FIGS. 1A-1C and the apparatus 20 ofFIG. 2. One difference of the apparatus 30 of FIGS. 3A and 3B is that asectioned relay lightpipe 34 is provided instead of the homogeneouslightpipe 14 of FIGS. 1A-1C and FIG. 2. The sectioned relay lightpipe 34of FIGS. 3A and 3B includes first 31 and second 32 slabs of ahomogeneous transparent material extending between proximal 34A anddistal 34B ends of the sectioned relay lightpipe 34 and running adjacentand parallel to each other. The first slab 31 may optionally includefirst 31A and second 31B portions, the second slab 32 being disposed inbetween the first 31A and second 31B portions of the first slab 31. Thefirst slab 31 may be configured for propagating the illuminating light17 from the proximal end 34A to the distal end 34B, and the second slab32 may be configured for propagating the signal light 18 from the distalend 34B to the proximal end 34A. The first slab 31 including the first31A and second 31B portions, and the second slab 32 may have e.g.rectangular cross sections, or alternatively the first slab 31 may havean annular cross section, and the second slab 32 may have an circularcross section surrounded by the annular cross section of the first slab31.

The first 31 and/or second 32 slabs may include at least one mirroredside 33 extending between the proximal 34A and distal 34B ends, for abetter separation of the illuminating light 17 and the signal light 18.Outer sides of the first slab 31 may also be mirrored for a betterretaining of the illuminating light 17 in the first slab 31. The firstslab 31 may be chiseled at the distal end 34B of the relay lightpipe 34,for concentrating the illuminating light 17 on the sample 11.

Referring to FIG. 4A, an apparatus 40A for obtaining a reflectionspectrum of a granular material, such as seeds, grains, sands, powders,etc., capable of flowing and mixing, is presented. Various fluidmaterials such as suspensions, emulsions, etc., may also be measured bythe apparatus 40A. The apparatus 40A includes the spectrometer 12equipped with the relay lightpipe 14 of FIGS. 1A-1C or FIG. 2. The relaylightpipe 34 of FIGS. 3A and 3B may also be used. The apparatus 40A mayfurther include a container 42 for holding granular or fluid material41, and a vibration transducer 43 operably coupled to the container 42for vibrating the container 42. The container 42 may include an open end39, or merely an opening for inserting the relay lightpipe 14 into thegranular or fluid material 41 for obtaining an optical spectrum of thegranular or fluid material 41. As the optical spectrum is beingcollected, the vibration transducer 43 may vibrate the container 42,thereby causing moving and/or mixing of the granular or fluid material41. The moving and/or mixing the granular or fluid material 41 under thedistal end 14B of the relay lightpipe 14 may result in averaging of thereflection spectra being collected, which may lessen the influence ofshape and position of individual particles (grains fluid-suspendedparticles, etc.) of the granular or fluid material 41 under the relaylightpipe 14, making the reflection spectra collected by thespectrometer 12 more reproducible. The larger the cross-section of therelay lightpipe 34, the larger averaging effect may be. In oneembodiment, the vibration transducer 43 may vibrate the granular orfluid material 41 directly.

For transreflection measurements, the container 42 may include anoptional window 45 at the bottom, and an additional light source 46 maybe optically coupled to the window 45, for illuminating the granular orfluid material 41 through the window 45 while the vibration transducer43 vibrates the granular or fluid material 41, thereby causing movingand mixing of the granular or fluid material 41.

Transmission spectra of the granular or fluid material 41 may also beobtained. Referring now to FIG. 4B, an apparatus 40B for obtaining atransmission spectrum of the granular or fluid material 41 may includethe spectrometer 12, a relay lightpipe 44, and the container 42 forholding the granular material. The vibration transducer 45 may beoperably coupled to the container 42 for vibrating the container 42, oralternatively the vibration transducer 43 may vibrate the granular orfluid material directly. The additional light source 46 may illuminatethe granular or fluid material 41 with illuminating light 47 through thewindow 45 while the vibration transducer 45 vibrates the container 42,thereby causing moving and mixing of the granular or fluid material 41.

The relay lightpipe 44 may include a slab of homogeneous transparentmaterial extending between proximal 44A and distal 44B ends andconfigured for collecting signal light 48 emanating from the mixing andmoving granular or fluid material 41 illuminated with the illuminatinglight 47, and conducting the signal light 48 from the distal end 44B tothe proximal end 44A, for delivery to the spectral engine 6 of thespectrometer 12. The relay lightpipe 44 enables the spectrometer 12 toobtain the transmission spectrum of the granular material 41 at adistance D from the granular or fluid material 41, e.g. 10 cm or more.

The vibration transducer 43 of the apparatuses 40A and 40B of FIGS. 4Aand 4B may vibrate the container 42 along a vertical axis 49, that is,along the length dimension of the relay lightpipe 14, or it may vibratethe container along a horizontal axis 48, that is, perpendicular to therelay lightpipe 14. The vibration transducer 43 may include a piezotransducer, an electromagnetic transducer, a rotating eccentric weight,or another suitable vibrating mechanism.

Turning to FIG. 5A with further reference to FIG. 1A, an apparatus 50Afor obtaining an optical spectrum of the flowing granular or fluidmaterial 41 is shown. The granular or fluid material 41 may flow in adirection indicated by an arrow 52. The apparatus 50 a is similar to theapparatus 10 of FIG. 1A, and a relay lightpipe 54 is analogous to therelay lightpipe 14 of FIG. 1A. A distal end 54B of the relay lightpipe54 may be slanted, so that the flow of the granular or fluid material 41impinges onto the slanted distal end 14B at an acute angle. Due to itsgeometry, the slanted distal end 54B exerts a pressure on the granularor fluid material 41 as the granular or fluid material 41 flows in thedirection indicated by the arrow 52, which may facilitate illuminationof the granular or fluid material 41 and/or the spectral datacollection. An optional cover 53 having a window 59 may be provided forthe relay lightpipe 54. For instance, where an aggressive medium 57 ispresent on top of the granular or fluid material 41, the cover 53 mayprotect the relay lightpipe 54 from corrosion by the aggressive medium57.

Referring to FIG. 5B with further reference to FIG. 5A, an apparatus 50Bfor obtaining an optical spectrum of the flowing granular or fluidmaterial 41 is similar to the apparatus 50A of FIG. 5A. The apparatus50B may further include an optical fiber bundle 55 extending between itsfirst 55A and second ends 55B. The first end 55A may be optically andmechanically coupled to the opening 15A (or transparent window) in theouter surface 13A of the housing 13, and the second end 55B may beoptically and mechanically coupled to the proximal end 54A of the relaylightpipe 54. The optical fiber bundle 55 may be used with some othertypes of relay lightpipes, for example the optical fiber bundle 55 maybe used in the apparatus 10 of FIG. 1A between the opening 15A and theproximal end 14A of the relay lightpipe 14. A bifurcated fiber bundle,not shown, may be used with the sectioned relay lightpipe 30 of FIGS.3A, 3B.

Referencing to FIGS. 6A and 6B with further reference to FIG. 1A, aself-calibrating apparatus 60 for obtaining a spectrum of the sample 11is similar to the apparatus 10 of FIG. 1A. A relay lightpipe 64 of theapparatus 60 extends between its proximal 64A and distal 64B ends. Therelay lightpipe 64 is generally similar to the relay lightpipe 14 of theapparatus 10 of FIG. 1A, one difference being that the relay lightpipe64 may include a first opening 61. The first opening 61 runs through therelay lightpipe 64 in a direction 62 transversal to the illuminatinglight 17. The apparatus 60 may further include a calibration element 63insertable into the first opening 61. The calibration element 63 mayinclude a reflectance reference section 65.

In FIGS. 6A and 6B, the calibration element 63 is shown inserted intothe first opening 61. In FIG. 6A, the reference section 64 is aligned,or registered, with the first opening 61, so as to reflect theilluminating light 17 back to the proximal end 64 a of the relaylightpipe 64 for detection by the spectrometer 12. The purpose of thereflectance reference section is to enable the spectrometer 12 to obtaina spectrum, preferably a reflection spectrum, of a known sample. In oneembodiment, the reflectance reference section 64 may include a whitediffuse reflector, for example a Lambertian reflector. More than onereflectance reference section 65 may be provided in the calibrationelement 63.

The calibration element 63 may further include a through section 66,which may be aligned, or registered, with the first opening 61 when thecalibration element 63 is inserted into the first opening. When thethrough section is registered with the first opening 61, theilluminating light 17 may propagate via the through section 66, so as toimpinge onto the sample 11. The signal light 18 propagates from thedistal end 64B, back via the through section 66, and is directed by thelightpipe 64 towards the spectrometer 12. In one embodiment, the throughsection 66 includes a transparent solid material, through which theilluminating light 17 and the signal light 18 may propagate.

In FIGS. 6A and 6B, the through section 66 and the reflectancereference, section 65 of the calibration element 63 are shown disposedproximate each other along the calibration element 63, that is, alongthe transversal direction 62. When a calibration is required, thecalibration element is shifted in the transversal direction 62 asillustrated by an arrow 67A in FIG. 6A. To take a measurement, thecalibration element 63 is shifted in the transversal direction 62 asillustrated by an arrow 67B in FIG. 6B. Other configurations arepossible, for example the calibration element 63 may generally have acircular cross-section for inserting into the matching opening 61, whichmay have a matching diameter. The calibration element 63 may base aportion with a square cross-section, not shown, with the reflectancereference section 65 being on one of the sides of the square portion, oron opposite sides of the square portion.

Referring now to FIG. 7, a method 70 for obtaining an optical spectrumof the sample 11, e.g. the granular material 41 or another material e.g.a solid or liquid material, may include a step 71 of providing thespectrometer 12 described above with reference to FIGS. 1A-1C, 2, and3A-3B. In a next step 72, the relay lightpipe 14 may be provided. Therelay lightpipe 14 may be configured for unconstrained propagation oflight in bulk of the relay lightpipe 14 between the proximal 14A anddistal 14B ends, as explained above. Alternatively the sectioned relaylightpipe 34 of FIGS. 3A and 3B may be provided.

In a next step 73, the relay lightpipe 14 is affixed to the housing 13so that the proximal end 14A is disposed adjacent the opening 15A ortransparent window, thereby optically coupling the relay lightpipe 14 tothe light source 16 and the spectral engine 6 of the spectrometer 12. Ina following step 74, the distal end 14B of the relay lightpipe 14 isbrought near, into a contact, or inserted into the sample 11. In a next,signal collection step 75, the illuminating light 17 is conducted withinthe relay lightpipe 14 from the proximal end 14A to the distal end 14Bfor illuminating the sample 11, and the signal light 18 emanating fromthe sample 11 illuminated with the illuminating light 17 is collected.The signal light 18 may include e.g. a portion of the illuminating light17 reflected by the sample 11, a fluorescence light, a phosphorescencelight, etc. The signal light 18 is conducted by the relay lightpipe 14back from the distal end 14B to the proximal end 14A and further to thespectral engine 6. In a next step 76, the optical spectrum of the sample11 is obtained by the spectrometer 12. The relay lightpipe 14 enablesthe optical spectrum to be collected at a distance from the sample 11. Acalibration may be performed before bringing the relay lightpipe 14 tothe sample 11 in the step 74, e.g. by using the self-calibratingapparatus 60 of FIGS. 6A and 6B.

When the sample 11 includes the granular material 41, the granularmaterial 41 may be vibrated in the container 42 (FIG. 4A) in the signalcollection step 75. When the sample 11 includes a hazardous material,e.g. a chemically aggressive substance, and the measurement involved aphysical contact between the relay lightpipe 14 and the sample 11, therelay lightpipe 14 may be disposed of in an optional step 77.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments andmodifications, in addition to those described herein, will be apparentto those of ordinary skill in the art from the foregoing description andaccompanying drawings. Thus, such other embodiments and modificationsare intended to fall within the scope of the present disclosure.Further, although the present disclosure has been described herein inthe context of a particular implementation in a particular environmentfor a particular purpose, those of ordinary skill in the art willrecognize that its usefulness is not limited thereto and that thepresent disclosure may be beneficially implemented in any number ofenvironments for any number of purposes. Accordingly, the claims setforth below should be construed in view of the full breadth and spiritof the present disclosure as described herein.

What is claimed is:
 1. An apparatus comprising: a container for holdinga sample, the container including a window that is positioned at abottom of the container; a vibration transducer, operably coupled to thebottom of the container, for vibrating the container, the vibrationtransducer being capable of vibrating both in a direction along avertical axis relative to the bottom of the container and in a directionalong a horizontal axis relative to the bottom of the container; and alight source optically coupled to the window, the light sourceilluminating the sample via the window while the vibration transducervibrates the container.
 2. The apparatus of claim 1, where the samplecomprises a granular or fluid material.
 3. The apparatus of claim 1,where the container further includes an opening to receive a relaylightpipe into the sample.
 4. The apparatus of claim 1, furthercomprising: a relay lightpipe that obtains an optical spectrum of thesample while the vibration transducer vibrates the container.
 5. Theapparatus of claim 1, further comprising: a relay lightpipe thatincludes a slab of homogenous transparent material extending between aproximal end of the relay lightpipe and a distal end of the relaylightpipe.
 6. The apparatus of claim 5, where the slab of homogenoustransparent material includes a lens element optically coupled to thedistal end of the relay lightpipe.
 7. The apparatus of claim 1, furthercomprising: a relay lightpipe to: collect signal light emanating frommixing and moving of the sample that is caused by vibrating the sample.8. The apparatus of claim 7, where the relay lightpipe is further to:conduct the signal light from a distal end of the relay lightpipe to aproximal end of the relay lightpipe.
 9. The apparatus of claim 8, wherethe distal end of the relay lightpipe is chiseled.
 10. The apparatus ofclaim 1, where the vibration transducer vibrates the container along thevertical axis that is along a length dimension of a relay lightpipe. 11.The apparatus of claim 1, where the vibration transducer vibrates thecontainer along the horizontal axis that is perpendicular to a relaylightpipe.
 12. The apparatus of claim 1, where the vibration transducercomprises one of: a piezo transducer, an electromagnetic transducer, ora rotating eccentric weight.
 13. A method comprising: vibrating, using avibration transducer, a container that includes a window that ispositioned at a bottom of the container, the vibration transducer beingoperably coupled to the bottom of the container, the vibrationtransducer being capable of vibrating both in direction along a verticalaxis relative to the bottom of the container and in a direction along ahorizontal axis relative to the bottom of the container, and thecontainer holding a sample; and illuminating, using a light sourceoptically coupled to the window, the sample via the window while thecontainer is vibrating.
 14. The method of claim 13, where the samplecomprises a granular or fluid material.
 15. The method of claim 13,further comprising: obtaining, using a relay lightpipe, an opticalspectrum of the sample while the container is vibrating.
 16. The methodof claim 13, further comprising: collecting, using a relay lightpipe,signal light emanating from mixing and moving of the sample that iscaused by vibrating of the container.
 17. The method of claim 16,further comprising: collecting, using a slab of homogenous transparentmaterial extending between a proximal end of the relay lightpipe and adistal end of the relay lightpipe, the signal light from the distal endof the relay lightpipe to the proximal end of the relay lightpipe. 18.The method of claim 17, where the distal end of the relay lightpipe islensed.
 19. The method of claim 17, where the slab of homogenoustransparent material includes a lens element optically coupled to thedistal end of the relay lightpipe.
 20. The method of claim 13, wherevibrating the container comprises: vibrating the container along thevertical axis that is along a length dimension of a relay lightpipe.